Noble metals have been widely applied in a multitude of ways in various industries or technical fields, in which platinum group metals are not dissolved in acids, even though dissolving ruthenium (Ru), rhodium (Rh) and iridium (Ir) with aqua regia is very difficult.
Regarding the dissolution of noble metals, the popular method is to subject the noble metals into anodic dissolution, or called electrolysis dissolution, in which an electrolyte containing various solutes or salts is commonly employed to dissolve noble metals such as ruthenium (Ru), rhodium (Rh) and iridium (Ir). Since the noble metals are very inert, they are difficult dissolved by the combination with the electrochemical dissolution and acidic dissolution. Electrochemical dissolution may not provide high efficiency but still better than other chemical methods.
Ruthenium-cobalt (Ru—Co)-based alloy is an important film material for being a middle layer of a perpendicular magnetic recording media. Moreover, Ru—Co-based alloy is also an important catalyst material for application in hydrogen generation of a water gas shift reaction in hydrogen energy industries. Because Ru—Co-based alloy itself has special purposes as aforementioned, Ru is a noble metal and Co is important for lithium batteries, it is necessary to develop a recovering method for Ru—Co-based alloy.
One of the methods of recovering noble metals from waste metals is combined with electrochemical dissolution and acidic or alkaline treatment. Typically, making the waste metals smaller in size can elevate dissolution efficiency of noble metals due to increase of the reaction surface. For example, it is found in the experiments of decomposition tests on the special example of S-816 scrap, a Re/Ta-free Co-based alloy (40+%) with high proportions of Cr (20%) and Ni (20%) as well as, inter alia, Fe, Nb, W and Mo in the 4% range. The use of sulphuric acid as a corrosive electrolyte medium at 7×10−5 Hz (polarity reversal every 4 hours) is in this case presented as being best suited to this type of scrap.
Moreover, other research is directed to an aqueous inorganic acid, preferably hydrochloric acid, which is advantageously used as the electrolyte, in the event that the superalloy powders based on the major alloy components nickel (Ni), cobalt (Co) and/or chromium (Cr) are used as the powder to be decomposed, in particular those which furthermore contain valuable material components such as Hf, Ta, Nb, Mo, W, Re and/or platinum group metals.
Furthermore, Mahmoud et al. propose a leaching process based on the ability of platinum-group metals to form stable chloro-complexes in acidic chloride solutions. Industrial catalyst losses were examined for the recovery of platinum (Pt), palladium (Pd), and rhodium (Rh) by leaching with a mixture of sulfuric acid and sodium chloride to avoid using aqua regia or autoclave conditions. Extraction of platinum and rhodium in 60% H2SO4 at 135° C. steadily increased with increasing NaCl concentrations reaching 95% and 85%, respectively, at 0.1 M NaCl after two hours. By comparison, palladium was dissolved more quickly but also reached 85% under the same conditions. (See M. H. H. Mahmound, “Leaching Platinum-Group Metals in a Sulfuric Acid/Chloride Solution” Journal of the Minerals, Metals and Materials Society 2003, April, 37-40.)
An additional method relates to the recovery of platinum group metals and, more particularly, to the recovery of platinum group metals from various sources (such as automobile catalysts) by roasting the source material with one or more of sulfuric acid, a sulfate and/or a bi-sulfate and with one or more halogen salt.
In consideration of a Ru—Co-based alloy with a high degree of hardness, large Ru—Co-based alloy bulk is necessarily subjected to pretreatment before recovery, in which the pretreatment is to smash or grind the large Ru—Co-based alloy bulk into smaller pieces or powder. However, the pretreatment usually makes the recovery process more complicated and expensive.
Similarly, the recovery equipments for size reduction of a Ru—Co-based alloy with a high degree of hardness are more expensive, complicated and often maintained due to quick consumption of cutting tools used in recovering Ru—Co-based alloy.
According to prior research results, they fail to anticipate or suggest the composition and concentration of the electrolyte solution and the current density with the electrochemical dissolution of Ru—Co-based alloy.